1. Field of the Invention
The present invention relates to the field of timing control methods and apparatus and, in particular, to a timing control mechanism for providing a copy of time, a stable frequency, and/or a signal to lock on to a remote point.
2. Background
Temporal relationships are an important aspect of the measurement and control of electronic systems. As such electronic systems become more complex and physically distributed, the accurate synchronization of time signals is increasingly necessary while at the same time difficult to achieve. To address the need for clock synchronization within network systems, the Institute for Electrical and Electronic Engineers (IEEE) adopted IEEE-1588 (“Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems”).
By way of example, telecommunications networks have migrated from being predominantly circuit-switched to being predominantly packet-switched. When the individual switching nodes of such networks and the circuits forming the links between them are not synchronized in a manner that makes them traceable to a common network clock, certain existing equipment will become isolated from the synchronization networks and may therefore cease to function correctly unless steps are taken to avoid this condition. Pursuant to IEEE-1588, a master-slave relationship is defined among the participating clocks communicating via the network. The slaves synchronize their local clocks to the master clock through an exchange of messages defined by IEEE-1588.
A drawback of the clock synchronization mechanism defined by IEEE-1588 is that it does not work well over a network in which nodes are separated by great distances, such as the Internet, or by networks that invoke significant message delay jitter that reduces the accuracy and stability of the slave clocks. A message communicated over such a network may pass through several repeaters, switches, and routers, thereby introducing random length delays. These random delays prevent the slave clocks from maintaining synchronization to the master clock within the required bounds.
Thus, there is a need for a timing control mechanism for a network that compensates for the random delays in the samples to be dynamically adjustable to suit the changing characteristics of the delay path (typically a network).